Zinc-air battery

ABSTRACT

A zinc-air cell, a battery which is a low weight, low volume, or higher energy system, or a combination thereof and an apparatus for recharging the same are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Divisional Application from U.S. application Ser.No. 15/011,777, filed on Feb. 1, 2016, which is a ContinuationApplication from U.S. application Ser. No. 13/516,125, filed on Jul. 16,2013, U.S. Pat. No. 9,252,616 which is a United States National PhaseApplication of PCT Application No. PCT/IL2010/001047, filed on Dec. 13,2010, claiming the benefit of U.S. Provisional Application No.61/286,151, filed on Dec. 14, 2009, which are all incorporated in theirentirety herein by reference.

FIELD OF THE INVENTION

This invention provides zinc-air cells, zinc-air batteries and anapparatus for recharging the same, which is a low weight, low volume, orhigher energy system, or a combination thereof.

BACKGROUND OF THE INVENTION

It is known that metal-air batteries present remarkable characteristicswhich make them suitable for a number of important uses and thatrechargeable zinc-air batteries are well known in the art. In oneapproach, the battery is recharged solely by application of electriccurrent, however the zinc electrode (in practically relevantlimited-electrolyte conditions), does not maintain a compact shape onrepeated charge-discharge cycling, either forming zinc dendrites, whichshort out the cell, or the electrode undergoes zinc shape change, wherethe zinc tends to redistribute over the lower part of the plate withconsequent capacity fading and stack deformation.

Air electrodes based on carbon bonded by polymer have limited life whenexposed to the rigors of charge-discharge cycling, especially on erosiveoxygen evolution on charge. The previous designs often needed also tocarry an electrolyte pump, excess zinc and excess electrolyte in thebattery as means to prolong cycle life, but this lowers attainableenergy densities to around 100-150 Wh/kg.

In another approach, the battery is mechanically refueled by replacingspent anodes and electrolyte in the cell each cycle and recycling spentanodes back to zinc anodes off-board in a recycling process. Energydensities of 250 Wh/kg have been achieved.

Air electrodes to date have limited cycle life when exposed to themassive physical shock of replacement of zinc anodes in each cell,electrolyte leakage is difficult to prevent in such adisassembly-structured system, and again the need for excess zinc andexcess electrolyte in the cell negatively impacts energy density.

To date, a high energy density zinc-air battery, with a useful minimumzinc and alkaline electrolyte quantity, which is compact andrechargeable is lacking.

SUMMARY OF THE INVENTION

This invention provides, in some embodiments, a zinc-air cell, batteryand apparatus for recharging the same, which achieves improvedenergy/weight and energy/volume for the system, is a low weight, lowvolume, or higher energy system, or a combination thereof.

In one embodiment, this invention provides an apparatus for charging azinc-air cell or zinc-air battery, said apparatus comprising:

-   -   a reservoir, said reservoir comprising:        -   a zinc-containing electrolyte fluid;    -   an export feed operationally connected to said reservoir;    -   a fluid drainer; and    -   optionally a second discharge reservoir;    -   whereby:    -   said apparatus is operationally connectible to said zinc-air        cell or zinc-air battery for which charging is desired;    -   said reservoir of said apparatus is located externally to a        device containing a zinc-air cell or zinc-air battery for which        charging is desired and said export feed allows for the delivery        of said zinc-containing electrolyte fluid from said reservoir to        said zinc-air cell or zinc-air battery for which charging is        desired;    -   said fluid drainer is operationally connectible to said device        containing said zinc-air cell or zinc-air battery and        facilitates draining of at least a portion of an electrolyte        fluid located in a discharged or not fully charged zinc-air cell        or zinc-air battery in said device; and    -   said drained electrolyte fluid is conveyed to said reservoir or        optionally said drained electrolyte fluid is conveyed to said        second discharge reservoir.

In some embodiments, the apparatus further comprises at least onepumping element, which pumping element facilitates delivery of saidzinc-containing alkaline electrolyte fluid from said reservoir to saidzinc-air cell or zinc-air battery for which charging is desired, orwhich pump facilitates draining of at least a portion of an electrolytefluid located in a discharged or not fully charged zinc-air cell orzinc-air battery in said device, or a combination thereof.

In some embodiments, the apparatus further comprises a power supply forapplying voltage which power supply is operationally connectible to saidzinc-air cell or zinc-air battery.

In some embodiments, the apparatus further comprises a controller formodulating fluid pressure, fluid flow, fluid capacity, electrolytetemperature, voltage, current, the zinc concentration in the electrolytesolution applied, or a combination thereof.

In some embodiments, any zinc-air cell may be used in conjunction withthe apparatuses of this invention.

In some embodiments, the zinc-air cell will comprise

-   -   at least one zinc incorporating structure as the anode of said        cell;    -   at least one porous structure capable of absorbing oxygen from        the air as the cathode of said cell;    -   a casing in which said anode and cathode are positioned further        comprising an electrolyte fluid; and    -   an inlet and outlet in said casing, whereby said inlet and        outlet are constructed so as to permit exchange of said        electrolyte fluid in said cell with an electrolyte fluid located        in an off-board reservoir;    -   wherein said anode and cathode are electrically connectible        across a load and wherein said zinc-containing electrolyte fluid        in said reservoir is comprised of zinc-oxide.

In some embodiments, according to this aspect, the zinc-air ceil willfurther comprise at: least a first separator positioned within said cellbetween said anode and said cathode.

In some embodiments, the zinc-air cell comprises:

-   -   a casing;    -   at least one porous structure capable of absorbing oxygen from        the air as the cathode of said cell placed within said casing;    -   a slurry consisting essentially of zinc and electrolyte solution        placed within said casing;    -   a separator positioned between said porous structure and said        slurry;    -   at least one current collecting electrode placed in said casing        and in contact with said slurry;    -   optionally comprising one or more porous tubes placed in said        casing and in contact with said slurry, facilitating electrolyte        solution passage there-through; and    -   comprising an inlet and outlet in said casing, whereby said        inlet and outlet are constructed so as to permit exchange of        said slurry, introduction and exchange of electrolyte fluid or a        combination thereof in said cell with a slurry, an electrolyte        fluid, or a combination thereof located in an off-board        reservoir.

In some embodiments, the solution may further comprise other elements,such as, for example, zinc oxide in solution, inhibitors for corrosion,extenders to allow maximum solubility of the zinc oxide, for example,such as sodium silicate, inert conductors, flow aids, gelling agents,and other materials, as will be appreciated by the skilled artisan. Insome embodiments, when zinc alloys are used in the cells as describedherein the solution may further comprise some of the components in thealloy, as well.

In some embodiments, in accordance with the invention, the sameprinciples described herein for an apparatus for recharging a zinc-airbattery may be adapted for other metal-air batteries, as well, forexample, when the cathode comprises a metal slurry in solution, suchslurry may comprise aluminum or iron in an alkaline potassium hydroxidesolution and the air cell would therefore be an iron-air or aluminum-aircell, which air cell would function as would a zinc-air cell, and whichmetal-air cell would be interchangeable in the apparatus and inaccordance with the methods of this invention. Other slurries based onaluminum, magnesium or silicon are feasible and electrolytes may beselected from KOH, NaOH, salt solutions and ionic liquids.

In some embodiments, the zinc-air cell comprises:

-   -   at least one zinc-containing anode;    -   at least one porous structure capable of absorbing oxygen from        the air as the cathode of said cell;    -   optionally at least a first separator positioned within said        cell between said anode and said cathode    -   a casing in which said anode and cathode are positioned, further        comprising an alkaline electrolyte fluid;    -   an inlet; and    -   an outlet;    -   wherein said inlet and said outlet are located within and        traverse said casing, whereby said inlet and outlet are        constructed so as to permit exchange of said electrolyte fluid        in said cell with an electrolyte fluid located in an off-board        reservoir and wherein said anode and cathode are electrically        connectible across a load and said zinc-containing electrolyte        fluid is comprised of zinc oxide.

In some embodiments, the apparatus further comprises an electricallyfloating metal substrate coated with an electrocatalyst, whichfacilitates hydrogen evolution in the presence of zinc, therebypreventing buildup of particulate zinc within said casing.

In some embodiments, the apparatus further comprises a temperatureregulator, which temperature regulator controls the temperature of theelectrolyte fluid in the reservoir.

In some embodiments, the apparatus further comprises a flow regulator,which flow regulator controls the flow speed or pressure of electrolytefluid conveyed from said reservoir or fluid conveyed to said reservoir.

In some embodiments, the apparatus further comprises a filter, whichfilter is operationally connected to said fluid drainer and therebyfilters electrolyte fluid conveyed from said air cell, said export feedand thereby filters electrolyte fluid conveyed to said air cell, or acombination thereof.

In some embodiments, the invention provides a method for recharging azinc-air cell or zinc-air battery, said method comprising:

-   -   contacting a zinc-air cell or zinc-air battery with an apparatus        as herein described, such that:        -   said export feed of said apparatus is operationally            connected to said zinc-air cell and electrolyte fluid can            thereby be conveyed from said reservoir to said zinc-air            cell; and        -   said fluid drainer is operationally connected to said            zinc-air cell and electrolyte fluid from said zinc-air cell            can be conveyed out of said zinc-air cell thereby;    -   promoting conveyance of zinc-containing electrolyte fluid from        said reservoir to said zinc-air cell via said export feed; and    -   promoting conveyance of electrolyte fluid from said zinc-air        cell to said apparatus via said fluid drainer.

In some embodiments, the apparatus further comprises a power supply andsaid method further comprises applying voltage to said zinc-air cell. Insome embodiments, the method further comprises applying voltage to saidzinc-air cell following conveyance of said zinc-containing electrolytefluid from said reservoir to said zinc-air cell via said export feed.

In some embodiments, this invention provides a zinc-air cell comprising:

-   -   a zinc-containing anode comprising:        -   at least one electrically conducting porous support for zinc            incorporation there-within;        -   a porous polymer-based mat positioned proximally to said            porous support; and    -   an outer coating, mesh or wire assembly positioned proximally to        said porous polymer-based mat and distal to said porous support        and comprising an electrocatalyst for hydrogen evolution in the        presence of zinc, at least one porous structure capable of        absorbing oxygen from the air as the cathode of said cell;    -   a casing in which said anode and cathode are positioned further        comprising an alkaline electrolyte fluid;    -   optionally an inlet and outlet in said casing, whereby said        inlet and outlet are constructed so as to permit exchange of        said electrolyte fluid in said cell with an electrolyte fluid        located in an off-board reservoir; and    -   optionally at least a first separator positioned within said        cell between said anode and said cathode    -   wherein said anode and cathode are electrically connectible        across a load.

In some embodiments this invention provides a metal-air cell comprising:

-   -   a casing comprising an inlet and an outlet;    -   at least one porous structure capable of absorbing oxygen from        the air as the cathode of said cell placed within said casing;    -   a slurry consisting of potassium hydroxide solution and zinc,        iron or aluminum placed within said casing;    -   a separator positioned between said porous structure and said        slurry;    -   elongated conductors placed in said casing and in contact with        said slurry;    -   at least one porous tube which is placed in said casing, in        contact with said slurry, and spans a said casing such that a        portion of said porous tube protrudes from said casing, wherein        said porous tube is so constructed so as to facilitate potassium        hydroxide solution passage there-through; and wherein said anode        and cathode are electrically connectible across a load and        whereby said inlet and outlet permit exchange of said slurry,        introduction and exchange of electrolyte fluid or a combination        thereof in said cell with a slurry, an electrolyte fluid, or a        combination thereof located in an off-board reservoir. In some        embodiments, according to this aspect, the metal-air cell may        further comprise at least one agitator.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the subject apparatuses, zinc air cells and zincair batteries are described herein with reference to the figureswherein:

FIG. 1 schematically depicts applications of a metal-air battery inaccordance with this invention.

FIG. 2 schematically depicts applications of the apparatuses/chargingstations in accordance with this invention.

FIG. 3 depicts a simple metal-air cell.

FIG. 4 depicts a simple metal-air cell operationally connected to anembodiment of an apparatus as herein described.

FIG. 5 depicts another embodiment of a metal air cell comprisingauxiliary electrodes, for use and incorporation with theapparatuses/methods of this invention.

FIG. 6A depicts a cross sectional view of an embodiment of a zinc aircell comprising a zinc/KOH slurry as the anode.

FIG. 6B depicts a longitudinal view of an embodiment of a zinc air cellcomprising a zinc/KOH slurry as the anode.

FIG. 7 depicts an embodiment of a layered anode of a metal air cell ofthis invention.

FIG. 8 depicts an embodiment of a refuelable slurry type primary cell ofthis invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides, in some embodiments, a system, battery and cellwhich may yield improved energy/′weight, or energy/volume. The inventionprovides, in some embodiments, for a minimal element, or in someembodiments, for a low volume metal-air cell, which is connectible to acharging station, which allows for a battery and metal-air cells to bedesigned as compact primary batteries, with their inherent higher energydensities, yet are fully rechargeable and thereby environmentallyfriendly and cost-effective.

Some embodied key cell features achieving high energy density are themetal inventory, for example, the zinc inventory, where little sparezinc may be needed in the cell to maintain design capacity rating, sincein each cycle the zinc may returned to essentially its pristine statefor the next discharge and the electrolyte and inter-electrode spacingmay be kept to the minimum, assuming a low volume cell design. In someembodiments, the electrolyte content may be kept as low as 0.5 cc-1cc/Ah, basically a starved electrolyte in the cell in which the celldischarge reaction product is mainly ZnO, see Eq. 1. According to thisembodiment, such apparatus and cell design provides an additionalbenefit in reducing the need for auxiliary elements, as discussedfurther herein below, in order to reach energy densities at the batterylevel (energy/unit weight) towards 350 Wh/kg, and energy per unit volume(specific energy) towards 800 Wh/L.2Zn+O₂=2ZnO  Eq. 1

The apparatus, methods, batteries and cells of this invention allow fora primary cell configuration, which in turn provides weight savings overprior art rechargeable zinc-air systems, also in terms of auxiliaryelements necessary on board the device in which the cell/battery isutilized. Such auxiliary elements may include, for example, a pump, heatmanagement system, water management system, CO₂ scrubbing systems or anyother auxiliary element typically seen in other onboard battery devices.

In accordance with the apparatus/system/batteries and cells of thisinvention, since the battery is returned to recharging-system eachcycle, where water, CO₂ laden electrolyte etc. can be treated and/orreplenished, such auxiliary systems can be dispensed with or be minimal.It should be noted that since the recharging-system comprises anoff-board electrolyte reservoir, to feed the cell on theelectrically/hydraulically recharge mode, the temperature controlmechanisms may be located off-board, on the recharging-system.

Thus in some embodiments, the invention provides a metal air cellcomprising:

-   -   at least one metal-containing anode;    -   at least one porous structure capable of absorbing oxygen from        the air as the cathode of said cell;    -   optionally at least a first separator positioned within said        cell between said anode and said cathode    -   a casing in which said anode and cathode are positioned, further        comprising an alkaline electrolyte fluid;    -   an inlet; and    -   an outlet;    -   wherein said inlet and said outlet are located within and        traverse said casing, whereby said inlet and outlet are        constructed so as to permit exchange of said electrolyte fluid        in said cell with an electrolyte fluid located in an off-board        reservoir and wherein said anode and cathode are electrically        connectible across a load.

In some embodiments, the invention provides a zinc air cell comprising:

-   -   at least one zinc-containing anode;    -   at least one porous structure capable of absorbing oxygen from        the air as the cathode of said cell;    -   optionally at least a first separator positioned within said        cell between said anode and said cathode    -   a casing in which said anode and cathode are positioned, further        comprising an alkaline electrolyte fluid;    -   an inlet; and    -   an outlet;    -   wherein said inlet and said outlet are located within and        traverse said casing, whereby said inlet and outlet are        constructed so as to permit exchange of said electrolyte fluid        in said cell with an electrolyte fluid located in an off-board        reservoir and wherein said anode and cathode are electrically        connectible across a load.

According to this aspect, and in some embodiments, the cell structure orbattery structure comprising the metal-air cells allows for regenerationor renewal of the metal anode, for example a zinc anode, by exchange, orpumping of the alkaline electrolyte solution. In some embodiments,according to this aspect, the alkaline electrolyte solution may comprisepotassium hydroxide. In some embodiments, the cell will comprise atleast one air electrode and a rechargeable minimal zinc-air cell asherein described. Such minimal zinc-air or metal-air cell is so termed,since the structure and arrangement is similar to that of a primarybattery placed within a device utilizing the cell/battery, yet suchcell/battery is rechargeable, by connection to an off-board apparatus,as herein described. The apparatus allows for the collection ofparticulates or aggregated by-products for example, sinking or presentat the bottom of the cells/batteries of the invention, and cleansing ofthe surfaces is enabled in the design of the cells/batteries of thisinvention.

According to this aspect, and in one embodiment, the renewal orregeneration of the cell/battery surfaces, including the anode surface,may be accomplished via application of the electrolyte solution,containing, for example, dissolved zinc oxide well below its maximumsolubility, which enables stripping of zinc oxide from the zinc anodefor example prior to zinc re-plating. In another embodiment, plating ofthe zinc may be accomplished by charging the electrodes when the cell isconnected to a charging station as described herein, concurrent with theapplication of the electrolyte solution.

Cells which may be suited for such recharging, yet are present in a lowvolume configuration in the systems, apparatuses/batteries of thisinvention include:

a zinc-air cell (I) comprising:

-   -   at least one zinc incorporating structure as the anode of said        cell:    -   at least one porous structure capable of absorbing oxygen from        the air as the cathode of said cell;    -   a casing in which said anode and cathode are positioned further        comprising an alkaline electrolyte fluid;    -   an inlet and outlet in said casing, whereby said inlet and        outlet are constructed so as to permit exchange of said        electrolyte fluid in said cell with an electrolyte fluid located        in an off-board reservoir; and    -   at least a first separator positioned within said cell between        said anode and said cathode    -   wherein said anode and cathode are electrically connectible        across a load.

a zinc-air cell (II) comprising:

-   -   a casing;    -   at least one porous structure capable of absorbing oxygen from        the air as the cathode of said cell placed within said casing;    -   a slurry consisting essentially of zinc and potassium hydroxide        solution placed within said casing;    -   a separator positioned between said porous structure and said        slurry;    -   optionally comprising at least one elongated current collecting        substrate placed in said casing and in contact with said slurry;    -   optionally comprising porous tubes placed in said casing and in        contact with said slurry, facilitating potassium hydroxide        solution passage there-through; and    -   optionally comprising an inlet and outlet in said casing,        whereby said inlet and outlet are constructed so as to permit        exchange of said slurry, introduction and exchange of        electrolyte fluid or a combination thereof in said cell with a        slurry, an electrolyte fluid, or a combination thereof located        in an off-board reservoir; and        wherein said anode and cathode are electrically connectible        across a load. In some embodiments, the electrolyte solution may        further comprise zinc oxide, inhibitors for corrosion,        antifoaming agents, extenders to allow maximum solubility of        zinc oxide, e.g. sodium silicate, inert conductors or flow aids,        and optionally alloyed components in the zinc, when the anode        comprises a zinc alloy slurry.

a zinc-air cell (III) comprising:

-   -   at least one zinc-containing anode;    -   at least one porous structure capable of absorbing oxygen from        the air as the cathode of said cell;    -   optionally at least a first separator positioned within said        cell between said anode and said cathode    -   a casing in which said anode and cathode are positioned, further        comprising an alkaline electrolyte fluid;    -   an inlet; and    -   an outlet;    -   wherein said inlet and said outlet are located within and        traverse said casing, whereby said inlet and outlet are        constructed so as to permit exchange of said electrolyte fluid        in said cell with an electrolyte fluid located in an off-board        reservoir and wherein said anode and cathode are electrically        connectible across a load.

FIG. 1 provides a scheme for the application of metal aircells/batteries envisioned for use in accordance with themethods/apparatuses/systems of this invention and FIG. 2 provides ascheme for the incorporation of the metal-air cell/batteries within theapparatuses of this invention to effect recharging low volumemetal-air/zinc-air batteries, in accordance with the methods of thisinvention.

Referring now to FIG. 3, a zinc air cell is basically designed inprimary (discharge only mode) with a useful low volume zinc and alkalineelectrolyte (KOH) quantity for the desired capacity, which makes for ahigh energy density. As depicted the zinc electrode 3-10 is the anodeand is positioned medially between two air electrodes 3-20, and aseparator 3-30 is placed between the zinc electrode and each airelectrode. The electrodes are placed in a casing, filled with a lowvolume of electrolyte solution 3-40.

In some embodiments, such zinc-air cells may be referred to herein as“minimal element zinc-air cells”, which will be understood to refer to azinc-air cell comprising a small spacing between electrodes, low volumeof electrolyte solution and minimal components necessary to operate thecell/battery and thereby achieve highest energy density possible for theconfiguration chosen.

In such a starved electrolyte condition on discharge, the zinc formszinc oxide (ZnO). The cell/battery, however, may be furtherhydraulically, operationally connected to an apparatus, which is locatedexternal to the device in which the battery/cell is found. The apparatuscomprises a reservoir of electrolyte solution (for example, KOH withdissolved zinc oxide) and optionally an off-board pump.

An embodiment of a connection of a schematic depiction of an apparatusof this invention is presented in FIG. 4. The electrolyte solution isconveyed through the cell, for example, an export feed 4-20operationally connected to the reservoir 4-10 conveys electrolyte in,while a fluid drainer 4-30 is operationally connected to the devicecontaining the zinc-air cell or zinc-air battery and facilitatesdraining of at least a portion of an electrolyte fluid 4-40 located in adischarged or not fully charged zinc-air cell or zinc-air battery insaid device. The draining of the native electrolyte contained in thezinc-air cell/battery may be concurrent with the conveyance of theelectrolyte fluid from the reservoir, or it may follow, or suchintroduction of electrolyte solution from the reservoir and drainage ofthe electrolyte solution from the battery/cell may be cycled, in a startand stop mode, and any of such means of introducing the electrolytefluid from the reservoir to the battery/cell and drainage of theelectrolyte fluid from the battery/cell may be envisioned to encompassan embodiment of the invention.

The electrolyte solution may be pumped through the cell/battery 4-50,and in some embodiments, charging current is passed through the cellconcurrently 4-60, or following an initial electrolyte solutionexchange, as described. Charging is passed through the cell in the usualway, i.e., zinc electrode negative, air electrode positive as depictedfor example in FIG. 4 (electrical connection to the right-hand airelectrode is not shown). Since the electrolyte is greatly in excess andflows through the cell, there is formed a well behaved uniformdendrite-free deposition of zinc on the plate (as if deposition hadoccurred under the optimum conditions of a plating bath). Desiredparameters of the deposit such as thickness and porosity can be adjustedbased on charging conditions and electrolyte additives, as is well knownin the art. Once the zinc has deposited, the hydraulic connection withthe external reservoir and its pump is broken, and the cell is readywith refreshed zinc electrode and remaining (starved) electrolyteinventory for high energy density discharge in primary mode. Such areplaceable energy battery is a candidate to work in tandem with aconventional electrically rechargeable power battery in a full EVsystem.

In some embodiments, the apparatus may comprise and a metal-air/zinc-aircell/battery may make use of a controller for the application ofcurrent/voltage to the systems as herein described.

In some embodiments, since zinc oxide is the discharge product and isreadily soluble in excess electrolyte, one use mode is to flow theexcess electrolyte through the cell before applying the charge current.According to this aspect, the zinc oxide on the plate can be rapidlycleaned off before electrical charging is commenced, making for betterzinc plate cyclability.

In some embodiments, a simple geometry KOH-inert support for the zinc,such as a nickel or nickel plated steel sheet or foil, suitablyprocessed, can be used in accordance with the invention. In someembodiments, a highly porous metallic support matrix, such as asintered, mesh, fibrous, foam or sponge structure, suitably processed,is to be incorporated, and making use of freely electrolyte permeable inflow-by or flow-through modes and the zinc deposit can uniformly buildup during charge. Such a conductive matrix offers, in some embodiments,a stable anode-cathode separation during discharge, while the matrixmaintains a more uniform electrical conductivity distribution asinsulating zinc oxide builds up on discharge. In some embodiments, theinvention may make use of air electrodes designed for discharge only,the cell may incorporate auxiliary electrodes situated between the zincelectrode and the air electrode (e.g. based on a lightweight catalyzedmesh for recharge, for example, as depicted in FIG. 5) 5-30. In thisembodiment, the cell comprises a zinc electrode 5-10, two airelectrodes, 5-20 and two auxiliary charging electrodes 5-30 applyingcurrent towards the zinc electrode on the charging mode.

Use of auxiliary electrodes may provide an added benefit, in someembodiments, of allowing for higher charge currents and thus faster cellrecharging. In some embodiments, simpler configurations may beenvisioned, where bi-functional type air electrodes may be used.

In some embodiments, a modified cell and charging scheme as describedherein may be envisioned.

In another embodiment, the zinc-air cell comprises

-   -   a casing comprising an inlet and an outlet;    -   at least one porous structure capable of absorbing oxygen from        the air as the cathode of said cell placed within said casing;    -   a slurry consisting of zinc and potassium hydroxide solution or        NaOH solution        -   placed within said casing;    -   a separator positioned between said porous structure and said        slurry;    -   elongated conductors placed in said casing and in contact with        said slurry;    -   at least one porous tube which is placed in said casing, in        contact with said slurry, and spans a said casing such that a        portion of said porous tube protrudes from said casing, wherein        said porous tube is so constructed so as to facilitate d        potassium hydroxide solution or NaOH solution passage        there-through; and        -   wherein said anode and cathode are electrically connectible            across a load and whereby said inlet: and outlet permit            exchange of said slurry, introduction and exchange of            electrolyte fluid or a combination thereof in said cell with            a slurry, an electrolyte fluid, or a combination thereof            located in an off-board reservoir.

According to this aspect and in some embodiments, the porous tube iscomprised of any alkaline resistant material, for example,polypropylene, Teflon, nylon, polyethylene, polyvinyl chloride,polystyrene, polyphenylene oxide etc.

In some embodiments, the elongated conductors are current collectingwires or strips. In some embodiments, an elongated conductor of thisinvention may be an open metallic or carbon based foam or mat thatentrains and provides conductive contact to zinc particles during thepumping into the cell of the slurry for recharge and during thesubsequent discharge.

According to this aspect, and in some embodiments, the active zincmaterial is a zinc powder/KOH or zinc powder/NaOH slurry, or other metalslurry as described herein, which can be pumped in and out of the cell.The elongated current collector for such a flowable anode slurry wouldbe an open wire brush-like structure 6-40 and the anode space wouldcontain, in some embodiments, at least one porous walled tube 6-50 (seeFIG. 6A, top view). As is depicted in this illustration, the airelectrodes 6-20 are positioned at the termini of the casing, withazinc/KOH-containing or zinc/NaOH-containing slurry localizedthere-between 6-10, and the elongated conductors 6-40 are positionedwithin the slurry, as is the porous walled tube 6-50. FIG. 6B shows alongitudinal view of an embodiment of this aspect of the invention,where a pair of separators 6-30 are positioned next to the slurry,wetted by the slurry but separating the air electrodes 6-20 from theslurry. The electrical connection to the right hand air electrode is notshown. Positioning of the current collector 6-40 and the porous walledtube 6-50 for electrolyte entry and exit for slurry renewal is shown.The positioning of the inlet 6-60 and outlet 6-70 within the casing isevident in this illustration, as well. It is also possible to include insuch cells/batteries, an additional porous substrate 6-80 or plate,underneath which is placed free electrolyte 6-90 and power may be takenfrom the terminals 6-100. Thus, in one embodiment, according to thisaspect, the cell may be flushed with electrolyte to be introduced, bothin the main compartment and the compartment created beneath the poroussubstrate or plate.

During cell discharge, the zinc in the slurry would convert to zincoxide as before. To carry out “recharge”, electrolyte from an externalreservoir would first be pumped through the spent anode via the porouswalled tubes, which would rapidly dissolve the zinc oxide component,loosening the slurry and enabling its facile pump-out from the cells.The cell would then be recharged simply by pumping in fresh slurry froma slurry reservoir without any electrical recharging needed. Accordingto this aspect, refueling can be quite fast (minutes). The spent slurryremoved from the cell would be externally regenerated by electrolysis ina regeneration cell, regenerating zinc power on the cathode (forexample, removable by periodic scraping) and evolving oxygen from aninert anode. The zinc powder would be reformed into fresh slurry bymixing with KOH, including additives, as necessary (for example,thickener, inert electrically conducting powder, etc.).

When externally regenerating zinc from a discharged slurry, the zincoxide discharge product is dissolved in excess electrolyte, and fromthis solution zinc powder can be regenerated electrolytically. Freshslurry can then be reformulated from the zinc powder by addingelectrolyte and any additives. In one electrolytic route, zinc isdeposited on the cathode of a regeneration cell and oxygen is evolvedfrom the anode in this cell. The cell reaction is:2ZnO=2Zn+O₂  Eq. 3.

In an alternative route for slurry regeneration from electrolyte, zincis deposited on the cathode of a regeneration cell as before, but theanode in that cell is a porous electrode for hydrogen oxidation. Thecell reaction is:ZnO+H₂=Zn+H₂O  Eq. 4The hydrogen would be normally supplied by reforming of natural gas andthe cell driven by a much lower potential than required in Eq. 3 andsuch a process is superior energetically to Eq. 3.

While Zinc/KOH slurries are described herein, it is noted thatadditional metal slurry/air cell configurations are possible, includingthe use of iron, aluminum, magnesium, silicon and others, as will beappreciated by the skilled artisan. Alternative electrolytes to KOH,such as NaOH, salt solutions or ionic liquids are also applicable, andrepresent contemplated embodiments for any aspect of the invention asherein described. In some embodiments, such electrolytes may beincorporated within any system as herein described, or inn someembodiments, such electrolytes may be incorporated within any air cellas herein described, or in some embodiments, such electrolytes may beincorporated within any slurry, as herein described. Where regenerationof the elemental components is not readily accomplishedelectrochemically, following slurry removal from the cell/battery,additional steps may be necessary and such steps/methods are well knownin the art.

In other embodiments, conventional polymer bonded carbon based airelectrodes and state of the art robust air electrodes whether of theprimary or bi-functional type, may be utilized and incorporated withinthe materials and methods of this invention.

In some embodiments, the invention provides therefore for a metal-aircell, which in some embodiments is a zinc-air cell(s) with low volumezinc and electrolyte inventory which are connected to an off-boardreservoir comprising an alkaline electrolyte solution, for example, KOHwith dissolved ZnO that is pumped through the cell during electricalrecharge, where the air electrodes are most simply bi-functional.

In some embodiments, the pumping stage precedes the charging stage toallow cleaning of the ZnO from the zinc electrode substrate. In someembodiments, when charging occurs, auxiliary electrodes (not the airelectrodes themselves) may be used to effect the charging, instead ofthe air electrodes.

In some embodiments, the cells/batteries for use in accordance with themethods/apparatuses of this invention will comprise an anode, which isnot a flat plate but rather a developed porous structure, for example,comprising a metal or metal alloy, which structure allows for fastcharging of the zinc (anode) substrate. In some embodiments, the anodeis a graphite/carbon sponge into which the zinc plates on charge.

In some embodiments, the cells/batteries for use in accordance with themethods/apparatuses of this invention comprise a primary zinc-air cellwith a high-capacity zinc deposit on the anode, only partiallydischarged each cycle, where the resultant ZnO product on the anode iscleaned off each time by flowing electrolyte from the reservoir, andonly requiring electrical recharge once every few cycles.

In some embodiments, the cells/batteries for use in accordance with themethods/apparatuses of this invention comprise a primary zinc-air cellwith a zinc powder/KOH anode slurry where the cell is recharged byfluidly replacing the spent zinc/KOH slurry anode with fresh slurry andthe spent slurry in the cell is loosened for pumping out (for off-boardregeneration) by exposure to electrolyte flowing through porous pipes inthe anode (for very fast recharge).

In some embodiments, the repeated plating and discharge of the zinc inthe cell, in using conventional metal-air/zinc-air cells, may result inmetallic zinc plated on the anode during charge to occasionallypartially detach from the anode to fall to the bottom of the cell. Sincemetallic zinc is not directly soluble in KOH it could interfere withelectrolyte transfer between cells on pumping, even causing a short.This could be dealt with (see FIG. 7) by affixing on the internal baseof a cell an electrically floating metal mesh coated with anelectrocatalyst for hydrogen evolution (e.g. catalytic metal orcatalytic metal oxide compositions as known in the art). Zinc particleson falling to the base of the cell will come into contact with the mesh,spontaneously oxidizing to ZnO in the cell electrolyte (along with somehydrogen evolution) and dissolve away, see Eq. 2,Zn+H₂O═ZnO(dissolves)+H₂  Eq. 2:

In some embodiments, the invention provides a zinc-air cell comprising

-   -   a zinc-containing anode comprising:        -   at least one electrically conducting porous support for zinc            incorporation there-within;        -   a porous polymer-based mat positioned proximally to said            porous support; and    -   an outer coating, mesh or wire assembly positioned proximally to        said porous polymer-based mat and distal to said porous support        and comprising an electrocatalyst for hydrogen evolution in the        presence of zinc at least one porous structure capable of        absorbing oxygen from the air as the cathode of said cell;    -   a casing in which said anode and cathode are positioned further        comprising an alkaline electrolyte fluid;    -   optionally an inlet and outlet in said casing, whereby said        inlet and outlet are constructed so as to permit exchange of        said electrolyte fluid in said cell with an electrolyte fluid        located in an off-board reservoir; and    -   optionally at least a first separator positioned within said        cell between said anode and said cathode    -   wherein said anode and cathode are electrically connectible        across a load.

In some embodiments, the porous polymer-based mat is comprised ofteflon, nylon, polypropylene or polyethylene, or in some embodiments,the mat is comprised of any alkaline resistant material which does nothave a connection to an external stimulus.

Referring to FIG. 7, the porous support for zinc incorporation is shown7-10, enveloped by a porous plastic mat 7-20, effectively wrapping theanode, as described, onto which is placed another outer coating or mesh7-30, for zinc dendrite removal.

Referring to FIG. 8, the invention provides another embodiment of afurther means to ensure a zinc-air cell with high energy density andminimal auxiliaries. According to this aspect, and in some embodiments,a self-contained cylindrical cell approach may be undertaken for arefuelable slurry type primary cell. The outer wall of the (vertical)cylinder comprises an air electrode 8-30 fitted inside with a separatorlayer 8-40 and then a close-placed open metal mesh 8-50 acting as anodecurrent collector and pressing against the separator. The cell in tubeform is fitted with a top placed valve 8-10 for filling the cell and abottom placed valve 8-80 for emptying the cell after discharge. The cellis filled with slurry of zinc particles 8-60 and limited volume KOHsolution with the zinc particle size selected from 50 microns up to afew millimeters. In the center of the cell is provided agitation means8-70 for example a paddle, impeller or worm of a lightweight materiallike plastic, whose axis passes via a seal 8-20 out of the top of thecell to a lightweight rotation-providing means such as a motor orturbine (not shown). The agitation means is operable on discharge butalso during cell drainage following discharge. During discharge theagitation drives the zinc particles to impact the current collectingmesh, enabling high currents and continuing ablation of the zinc oxidedischarge product on the surface of the zinc particles. Similarly ondrainage the agitation helps remove the viscous discharge products inthe cell. This cell approach is applicable to use of primary typeconventional polymer-bonded carbon-based air electrodes or state of theart robust air electrodes. In a multicell battery it is envisioned thatmany electrically connected standalone tubes of this type could beexternally accessed for rapid filling and emptying with slurry at acharging station without the need for plumbing between tubes, a slurrystorage tank or an onboard slurry pump.

In some embodiments, the invention provides an apparatus for charging azinc-air cell or zinc-air battery, said apparatus comprising:

-   -   a reservoir, said reservoir comprising:        -   a zinc-containing alkaline electrolyte fluid;    -   an export feed operationally connected to said reservoir;    -   a fluid drainer; and    -   optionally a second discharge reservoir;

whereby:

-   -   said apparatus is operationally connectible to said zinc-air        cell or zinc-air battery for which charging is desired;    -   said reservoir of said apparatus is located externally to a        device containing a zinc-air cell or zinc-air battery for which        charging is desired and said export feed allows for the delivery        of said zinc-containing alkaline electrolyte fluid from said        reservoir to said zinc-air cell or zinc-air battery for which        charging is desired;    -   said fluid drainer is operationally connectible to said device        containing said zinc-air cell or zinc-air battery and        facilitates draining of at least a portion of an electrolyte        fluid located in a discharged or not fully charged zinc-air cell        or zinc-air battery in said device; and    -   said drained electrolyte fluid is conveyed to said reservoir or        optionally said drained electrolyte fluid is conveyed to said        second discharge reservoir.

The apparatus of this invention incorporates a reservoir, whichreservoir comprises a zinc-containing alkaline electrolyte fluid. Itwill be appreciated by the skilled artisan, that the term“zinc-containing alkaline electrolyte fluid” will be any appropriateelectrolyte fluid for use in accordance with the described zinc-aircells or batteries as herein described, which contains an appropriateform of zinc or a zinc-containing compound, for example, zinc oxide. Itwill be appreciated that the term “zinc-containing alkaline electrolytefluid” for incorporation within the apparatuses of this invention maycontain elemental zinc or zinc oxide, as will be appropriate andsuitable for the corresponding zinc-air cell or zinc-air battery beingattached to an apparatus as herein described, and as will be understoodby the skilled artisan.

In some embodiments, for example as depicted in FIG. 4 the electrolytefluid conveyed to the metal-air cell from the reservoir is concurrentwith drainage of electrolyte fluid to the same reservoir, or in someembodiments, the drained electrolyte fluid is optionally drained to asecond discharge reservoir.

The term “reservoir” as used herein refers to any receptacle capable ofstoring an alkaline electrolyte solution for delivery to themetal-air/zinc-air cells as herein described. In some embodiments, suchreservoir is envisioned as being located in a service station, forrecharging multiple metal-air/zinc-air cells, as needed, with a volumeand dimension to be feasible for mass usage. In some embodiments, suchreservoir is bounded by an appropriate material to prevent leakage ofthe solution, and in some embodiments, such reservoir may be storedunder- or above-ground, as needed.

In some embodiments, the drainer is a pipe, tubing, siphon or othermeans by which fluid may be drawn from the indicated source and conveyedto the desired container. In some embodiments, the drainer may beconnected to a pump to speed fluid drainage, or in some embodiments, thedrainer may be further operationally connected to a filter, a converter,or other materials and then delivered to the desired repository.

In some embodiments, the export feed is similarly a pipe, tubing, siphonor other means by which fluid may be delivered to the metal-air orzinc-air cell/battery from the reservoir. In some embodiments, theexport feed may also be connected to a pump, a filter, or othermachinery to aid in the delivery of electrolyte fluid of a desiredcontent and for example, purity.

In some embodiments, both the export feed and the drainer are connectedto an inlet and outlet, respectively, in a metal-air/zinc-aircell/battery via a valve means, which regulates the flow of electrolytefluid into and out of the metal-air/zinc-air cell/battery.

It is to be understood that the metal-air/zinc-air cell/battery may beany appropriate metal-air/zinc-air cell/battery, including anyembodiment described and/or exemplified herein, and represents anenvisioned aspect of this invention. Any metal-air/zinc-air cell/batteryknown in the art may be utilized in accordance with the apparatusesand/or methods of this invention, and may be modified in someembodiments, to be more compacted versions of the same, and used inaccordance with the invention described herein.

In some embodiments, when the apparatuses of this invention areoperationally connected to an embodiment of the metal-air/zinc-aircell/battery as described herein, for example, in FIG. 6, or otherembodiments of such metal-air/zinc-air cell/battery, which make use of azinc-KOH containing slurry as the anode of the metal-air/zinc-aircell/battery, then the export feed and drainer will be of a material andsized so as to be appropriate for exchange of the slurry, as hereindescribed.

In some embodiments, in applying the metal-air/zinc-air cell/battery tothe apparatuses of this invention, any appropriate concentration ofelectrolyte solution is envisioned, and some exemplified concentrationsof the aqueous KOH envisioned, as common for many alkaline batterysystems, is in the range 20-45 wt %. ZnO normally dissolves chemicallyin such solutions to the extent of 100 gm/L or, if resulting from zincanode discharge in a cell and helped by dissolved extender additivessuch as sodium silicate, can reach 200 gm/L. In some embodiments, thesolution fed to the cell/battery from the reservoir during rechargewould have lower concentrations than these solubility limits, more akinto alkaline zinc plating baths, and the ZnO level may be desired to bemaintained between 10-50 gm/L to maintain good plating quality and theability to be a good dissolving medium of zinc oxide discharge productin the cell anodes.

The reservoir would be changing in zinc ion content between these outerlimits, depending on the reservoir size and number of cells/batteriesbeing serviced, for example between maximum 50 gm/L before thecell/battery is charged, and minimum 10 gm/L after the battery ischarged. The solution could advantageously be preheated (ZnO dissolvesfaster than in cold solutions), and may in some embodiments, furthercontain additives, for example to achieve and maintain desirable zincplating characteristics such as porosity, and to inhibit self dischargeon-stand of the zinc anode. In some embodiments the reservoir could bekept relatively compact by incorporating a filter containing solid phasezinc oxide through which KOH solution is optionally passed in order toreach the desired dissolved zinc oxide concentration.

In some embodiments, the solution composition would be maintained withinspecified limits at the off-board charging station and buildup ofimpurities (such as carbonates, impurity metal ions) could be preventedat the reservoir level.

In some embodiments, the apparatus may further comprise a temperatureregulator. which temperature regulator controls the temperature of theelectrolyte fluid in the reservoir.

In some embodiments, the apparatus may further comprise a flowregulator, which flow regulator controls the flow speed or pressure ofelectrolyte fluid conveyed from said reservoir or fluid conveyed to saidreservoir.

In some embodiments, the apparatus may further comprise a a filter,which filter is operationally connected to said fluid drainer andthereby filters electrolyte fluid conveyed from said air cell, saidexport feed and thereby filters electrolyte fluid conveyed to said aircell, or a combination thereof.

It is to be understood that any combination of the embodied apparatusesand metal-air or zinc-air cells/batteries as described herein may becombined and represent envisioned aspects of this invention.

In some embodiments, this invention provides a method for recharging azinc-air cell or zinc-air battery, said method comprising:

-   -   contacting a zinc-air cell or zinc-air battery with an apparatus        of this invention, such that:        -   said export feed of said apparatus is operationally            connected to said zinc-air cell and electrolyte fluid can            thereby be conveyed from said reservoir to said zinc-air            cell; and        -   said fluid drainer is operationally connected to said            zinc-air cell and electrolyte fluid from said zinc-air cell            can be conveyed out of said zinc-air cell thereby;    -   promoting conveyance of zinc-containing electrolyte fluid from        said reservoir to said zinc-air cell via said export feed; and    -   promoting conveyance of electrolyte fluid from said zinc-air        cell to said apparatus via said fluid drainer;

In some embodiments, the air cell comprises a zinc anode and the methodstrips accumulated zinc oxide from said anode, as described and embodiedherein.

In some embodiments, when the electrolyte fluid conveyed from saidreservoir to said air cell is a zinc-containing slurry and saidelectrolyte fluid conveyed from said zinc-air cell to said apparatus isa zinc-containing slurry, then the elements of the apparatus will beappropriate to accommodate the delivery and drainage of such slurry.

In some embodiments, the apparatus further comprises a power supply andsaid method further comprises applying voltage to said zinc-air cell. Insome embodiments, the voltage is applied following a pre-run ofelectrolyte fluid to strip accumulated ZnO from the anodes, as describedherein.

In some embodiments, the zinc-air cell comprises auxiliary electrodesand said power supply applies voltage to said auxiliary electrodes. Insome embodiments, the apparatus further comprises a temperatureregulator and said temperature regulator controls a temperature of saidelectrolyte fluid conveyed from said reservoir. In some embodiments, thezinc-air cell comprises a zinc plated metal anode, and said methodpromotes re-plating of said anode with zinc.

In some embodiments, the apparatus further comprises a scrubberoperationally connected to said reservoir, and other elements known andused in the art for recharging metal-air/zinc-air cells/batteries.

In some embodiments, the invention is applicable to all-electriczero-emission vehicles in fleet or individual use. These vehicles may bepowered by a high energy zinc-air battery requiring periodic stationcharging, which may contain the apparatuses according to the presentinvention (e.g. zinc-air 80 kWh, 200 kg), in tandem with a small powerbattery (e.g. Li-ion 10 kWh, 125 kg) that can accept home or workcharging as well as regenerative braking. Such a combination will allowa range of 40 km with the lithium-ion battery alone and 400 km with bothbatteries. In some embodiments, the Li-ion battery can deal with shorttrips, and for long trips the zinc-air battery would be used.

To recharge the zinc-air battery, the vehicle would, in someembodiments, enter a battery exchange station and have its batterymechanically replaced. It can be appreciated that the exchange stationmay be selected according to the route taken and alerted to theimpending battery exchange.

At the station the batteries could be recharged on site, ifinfrastructure is available, or in some embodiments, dischargedbatteries may be transported on a daily basis for recharging to adedicated urban recharge center.

At the urban recharge center batteries may be connected to rechargingmachines incorporating the apparatuses of this invention. Theserecharging machines would be designed according to the type of zinc-airbattery sent for recharge.

In the electrically recharged type of the present invention, batterycells would be individually connected to electrolyte pumped from anelectrolyte reservoir, and electrical charging commenced. This chargingwould take 1-5 hours and preferably be carried out using off-peakelectricity.

In the slurry replacement zinc-air battery of the present invention,machines would replace slurry in battery cells. This slurryreplenishment would take 10-30 minutes to provide a fresh battery anddischarged slurry would be processed on site by electrochemicalregeneration, preferably carried out using off-peak electricity andhydrogen

The examples provided herein-below are provided for illustrativepurposes alone and are not to be construed in any way as limiting theinvention.

While various embodiments of the present invention have been presented,it is possible to use various alternatives, modifications andequivalents. It is to be understood that any feature described herein,may be combined with any other feature described herein. It is to beunderstood that the article “a”, or “an” refers to a quantity of one ormore of the item following the article, except where expressly statedotherwise.

The following examples are intended to illustrate but not limit thepresent invention.

EXAMPLES Example 1

A zinc-air cell was constructed from two bi-functional air electrodes(10 cm×10 cm×0.1 cm thick) flanking a central zinc anode (as in FIG. 1).The air electrodes were edge-bonded using epoxy to a narrow U-shapedplastic profile such that the internal cell volume was about 40 cc andthe cell, which was fitted with electrolyte inlet and outlet vents, wasclosed with a plastic cover. The zinc anode support was a centrallyplaced nickel mesh (10 cm×10 cm×0.05 cm thick), 20 holes per cm, thathad been flash coated with indium to ensure an adherent zinc coating onzinc electroplating and inhibition of zinc self-discharge. Celgard(trademark) microporous polypropylene separators were bonded at theedges of the air electrodes inside the cell to prevent anode/cathodeshorting. On the base of the cell was bonded a nickel mesh coated withporous nickel as hydrogen evolution electrocatalyst in order to digestany occasional zinc particles falling from the anode. The initialspacing between air and zinc electrodes was about 1 mm and 30 ccelectrolyte (30 wt % KOH containing 50 gm/L dissolved ZnO) was used inthe cell. For charging the cell was hydraulically connected (using filltubes connected with the inlet and outlet vents) to a large externalelectrolyte reservoir (2 L of 30 wt % KOH containing 50 g/L dissolvedzinc oxide at 50 deg C.) that was pumped through the cell using anexternal pump at a pumping rate of 5 cc/minute. The cell electrodes wereconnected up to a DC power supply and the cell charged at 12 A. After5.511 a grey colored, compact, porous, uniform deposit of metallic zinchad built upon the anode support. The electrolyte circulation system wasdisconnected from the cell at this stage and the cell was discharged at10 A in static air using only the electrolyte that remained in the cell.The cell OCV was 1.45 V and the cell provided 50 Ah at an averageworking voltage of 1.25V till a cutoff of 0.9V, and it could be seenthat the anode had changed in appearance to the white color of zincoxide. To recharge the cell the electrolyte circulation system wasreconnected as before but electrolyte was flowed for 10 minutes beforecommencing electrical recharge in order to remove residual zinc oxidefrom the anode support. Following electrical recharge as before, thecell ocv was 1.45V and the cell provided again 50 Ah at an averageworking voltage of 1.25V till a cutoff of 0.9V, showing the goodrechargeability of the system. Energy density of the cell was 350 Wh/kgand energy per volume 800 Wh/kg.

Example 2

A zinc-air cell was constructed from two primary air electrodes (10cm×10 cm×0.1 cm thick) flanking a central zinc anode (as in FIG. 3). Theair electrodes were edge-bonded using epoxy to a narrow U-shaped plasticprofile such that the internal cell volume was about 50 cc and the cell,which was fitted with electrolyte inlet and outlet vents, was closedwith a plastic cover. The zinc anode support was a centrally placedsteel fiber-based porous plaque (10 cm×10 cm×0.3 cm thick), that hadbeen flash coated with indium to ensure an adherent zinc coating on zincelectroplating and inhibition of zinc self discharge. Between the airelectrodes and the zinc anode were two auxiliary charging nickel meshelectrodes that had been coated with an electrocatalyst for oxygenevolution, and these were wrapped in a layer of Celgard (trademark)microporous polypropylene separators to prevent anode/cathode shorting.On the base of the cell was bonded a nickel mesh coated with porousnickel as hydrogen evolution electrocatalyst, in order to digest anyoccasional zinc particles falling from the anode. The spacing betweenair and zinc electrodes was about 1 mm and 50 cc electrolyte (30 wt %KOH containing 50 gm/L dissolved ZnO) was used in the cell. For chargingthe cell was hydraulically connected (using fill tubes connected withthe inlet and outlet vents) to a large external electrolyte reservoir (5L of 30 wt % KOH containing 50 g/L dissolved zinc oxide at 50 deg C.)that was pumped through the cell using an external pump at a pumpingrate of 30 cc/minute. The zinc and auxiliary charging electrodes wereconnected up to a DC power supply and the cell charged at 50 A. After2.2 h a grey colored, compact, porous, uniform deposit of metallic zinchad built up within the anode support. The electrolyte circulationsystem was disconnected from the cell at this stage and the cell wasdischarged at 20 A using flowing air and only the electrolyte thatremained in the cell. The cell ocv was 1.45V and the cell provided 100Ah at an average working voltage of 1.25V till a cutoff of 0.9V, and itcould be seen that the anode had changed in appearance to the whitecolor of zinc oxide. To recharge the cell the electrolyte circulationsystem was reconnected as before but electrolyte was flowed for 20minutes before commencing electrical recharge in order to remove zincoxide from the anode support. Following electrical recharge as before,the cell ocv was 1.45V and the cell provided again 100 Ah at an averageworking voltage of 1.25V till a cutoff of 0.9V, showing the goodrechargeability of the system. Energy density of the cell was 400 Wh/kgand energy/volume was 1000 Wh/L.

Example 3

A zinc-air cell was constructed from two primary type air electrodes (10cm×10 cm×0.1 cm thick) flanking a central zinc anode slurry (as in FIG.4). The air electrodes were edge-bonded using epoxy to a narrow U-shapedplastic profile such that the internal cell volume was about 80 cc andthe cell, which was fitted with slurry inlet and outlet vents, wasclosed with a plastic cover. Celgard (trademark) microporouspolypropylene separators were bonded at the edges of the air electrodesinside the cell to prevent anode/cathode shorting. The anode slurryfilled the volume between the two air electrodes and was introduced intothe cell from a dosing type slurry pump in five seconds. It wascomprised of a suspension of zinc powder (66 wt %) in 34 wt % ofelectrolyte (30 wt % KOH containing dissolved ZnO 50 g/L). The anodecurrent collector was a brush type structure of nickel wires that dippedinto the slurry, where the wires had been flash coated with indium inorder to restrict self discharge of the zinc anode. Also dipping in theslurry were 4 tubes of porous plastic. The cell was discharged at roomtemperature at 10 A in static air. The cell OCV was 1.45V and the cellprovided 50 Ah at an average working voltage of 1.25V till a cutoff of0.9V. The discharged slurry was now more viscous than before dischargeand was difficult to remove from the cell, but on passing electrolyte at50 deg C. for 5 minutes through the porous tubes in the anode thedischarged slurry was loosened and the slurry could be pumped out usingthe slurry pump. From the cell discharge products slurry could beregenerated electrochemically. A fresh charge of slurry was transferredinto the cell and discharge recommenced. Again, the cell OCV was 1.45Vand the cell provided 50 Ah at an average working voltage of 1.25V tilla cutoff of 0.9V, showing the good recyclability of the system. Theenergy density of the cell was 400 Wh/kg, and energy per volume 800Wh/L.

While the disclosure has been illustrated and described, it is notintended to be limited to the details shown, since various modificationsand substitutions can be made without departing in any way from thespirit of the present disclosure. As such, further modifications andequivalents of the invention herein disclosed can occur to personsskilled in the art using no more than routine experimentation, and allsuch modifications and equivalents are believed to be within the spiritand scope of the disclosure as defined by the following claims.

What is claimed is:
 1. An apparatus for charging a zinc-air cell orzinc-air battery, said apparatus comprising: a reservoir comprising azinc-containing electrolyte fluid; an export feed operationallyconnected to said reservoir; a fluid drainer; whereby: said apparatus isoperationally connectible to said zinc-air cell or zinc-air battery forwhich charging is desired; said reservoir of said apparatus is locatedexternally to said zinc-air cell or zinc-air battery for which chargingis desired and said export feed allows for the delivery of saidzinc-containing electrolyte fluid from said reservoir to said zinc-aircell or zinc-air battery for which charging is desired; said fluiddrainer is operationally connectible to said zinc-air cell or zinc-airbattery and facilitates draining of at least a portion of an electrolytefluid located in a discharged or not fully charged zinc-air cell orzinc-air battery; and said drained electrolyte fluid is conveyed to saidexternal reservoir or to a discharge reservoir; wherein said zinc-aircell comprising: a casing; at least one porous structure capable ofabsorbing oxygen from the air as the cathode of said cell placed withinsaid casing; a slurry consisting essentially of zinc and electrolytesolution placed within said casing; a separator positioned between saidporous structure and said slurry; at least one current collectingelectrode placed in said casing and in contact with said slurry; aninlet and outlet in said casing; whereby said inlet and outlet areconstructed so as to permit exchange of said slurry, introduction andexchange of electrolyte fluid or a combination thereof in said cell witha slurry, an electrolyte fluid, or a combination thereof located in saidreservoir; a) wherein said zinc-air cell further comprises at least oneelectro-conducting porous support for zinc incorporation there-withinwherein said porous support comprises a metal or a metal alloy orgraphite/carbon sponge; or b) wherein said zinc-air cell furthercomprises a porous polymer-based mat positioned proximally to saidporous support wherein said porous polymer-based mat is comprised ofpolytetrafluoroethylene, nylon, polypropylene or polyethylene, and has athickness of between 30-1000 μm; or c) wherein said zinc-air cellfurther comprises an agitator; or d) wherein said zinc-air cell furthercomprises at least one porous tube which is placed in said casing, incontact with said slurry, and spans said casing such that a portion ofsaid porous tube protrudes from said casing; wherein said porous tube isso constructed so as to facilitate alkaline electrolyte passagethere-through; or e) a combination of two or more of a) through d). 2.The apparatus of claim 1, wherein said slurry comprises metallic zinc ata concentration of 15-40% by volume.
 3. The apparatus of claim 1,wherein said slurry contains potassium hydroxide in aqueous solution ata concentration of 25-45 w/w %.
 4. The apparatus of claim 1, whereinsaid apparatus is operationally connected to a battery comprising two ormore of said zinc-air cells.
 5. The apparatus of claim 4, wherein saidtwo or more zinc-air cells are hydraulically connected.
 6. The apparatusof claim 1, wherein said zinc-containing alkaline electrolyte fluid insaid reservoir is in the form of a slurry.
 7. The apparatus of claim 1,wherein said apparatus further comprises a regeneration unitoperationally connected to said reservoir, said regeneration unitcomprising: a cathode for zinc deposition; and an anode for hydrogenoxidation.
 8. The apparatus of claim 1, wherein said zinc-air cellfurther comprises an electrically floating mesh located at the bottom ofsaid cell, said mesh facilitates the collection of particulates oraggregated by-products sinking or present at the bottom of said cell,and cleansing of the surfaces of said cell.
 9. A method for recharging azinc-air cell or zinc-air battery, said method comprising: contacting azinc-air cell or zinc-air battery with the apparatus of claim 1, suchthat: said export feed of said apparatus is operationally connected tosaid zinc-air cell and electrolyte fluid can thereby be conveyed fromsaid reservoir to said zinc-air cell; and said fluid drainer isoperationally connected to said zinc-air cell and electrolyte fluid fromsaid zinc-air cell can be conveyed out of said zinc-air cell thereby;promoting conveyance of zinc-containing electrolyte fluid from saidreservoir to said zinc-air cell via said export feed; and promotingconveyance of electrolyte fluid from said zinc-air cell to saidreservoir or to a second discharge reservoir via said fluid drainer; andwherein said electrolyte fluid conveyed from said reservoir to said aircell is a zinc-containing slurry and said electrolyte fluid conveyedfrom said zinc-air cell to said reservoir or to a second dischargereservoir is a zinc-containing slurry.
 10. The method of claim 9,wherein said apparatus further comprises an agitator.
 11. The method ofclaim 9, wherein said apparatus further comprises a power supply, saidzinc-air cell comprises auxiliary charging electrodes and said powersupply applies current to said auxiliary electrodes.
 12. The method ofclaim 11, wherein said power supply comprises a DC charger.
 13. Themethod of claim 9, wherein said apparatus further comprises aregeneration unit operationally connected to said reservoir, saidregeneration unit comprising: a cathode for zinc deposition; and ananode for hydrogen oxidation; wherein said method comprising zincregeneration from zinc oxide in said regeneration unit, said zincregeneration comprises the formation of zinc on said cathode and theoxidation of hydrogen on said anode.
 14. The method of claim 13, whereinsaid hydrogen is supplied to said anode by reforming of natural gas. 15.An apparatus for charging a zinc-air cell or zinc-air battery, saidapparatus comprising: a reservoir, said reservoir comprising: i. analkaline electrolyte fluid containing dissolved zinc oxide; and ii.solid phase zinc oxide; an export feed operationally connected to saidreservoir; a fluid drainer; whereby: said apparatus further comprisingand operationally connectible to said zinc-air cell or zinc-air batteryfor which charging is desired; said reservoir of said apparatus islocated externally to said zinc-air cell or zinc-air battery for whichcharging is desired and said export feed allows for the delivery of saidalkaline electrolyte fluid containing dissolved zinc oxide from saidreservoir to said zinc-air cell or zinc-air battery for which chargingis desired; said fluid drainer is operationally connectible to saidzinc-air cell or zinc-air battery and facilitates draining of at least aportion of an electrolyte fluid located in a discharged or not fullycharged zinc-air cell or zinc-air battery in said device; and saiddrained electrolyte fluid is conveyed to said reservoir or said drainedelectrolyte fluid is conveyed to a second discharge reservoir; whereinsaid zinc-air cell or zinc-air battery comprising: a casing; at leastone porous structure capable of absorbing oxygen from the air as thecathode of said cell placed within said casing; an anode placed withinsaid casing; an inlet and outlet in said casing;  whereby said inlet andoutlet are constructed so as to permit introduction and exchange of saidelectrolyte fluid in said cell with an electrolyte fluid, located insaid reservoir, wherein: said apparatus further comprises a regenerationunit operationally connected to said reservoir, said regeneration unitcomprising: a cathode for zinc deposition; and an anode for hydrogenoxidation; and/or wherein: said zinc-air cell further comprises anagitator.
 16. The apparatus of claim 15, wherein said zinc-air cellfurther comprises a floating mesh, said mesh facilitates the collectionof particulates or aggregated by-products sinking or present at thebottom of said cell and cleansing of the surfaces of said cell.
 17. Amethod for recharging a zinc-air cell or zinc-air battery, said methodcomprising: contacting a zinc-air cell or zinc-air battery with theapparatus of claim 15, such that: said export feed of said apparatus isoperationally connected to said zinc-air cell and electrolyte fluid canthereby be conveyed from said reservoir to said zinc-air cell; and saidfluid drainer is operationally connected to said zinc-air cell andelectrolyte fluid from said zinc-air cell can be conveyed out of saidzinc-air cell thereby; promoting conveyance of said alkaline electrolytefluid from said reservoir to said zinc-air cell via said export feed;and promoting conveyance of electrolyte fluid from said zinc-air cell tosaid reservoir or to a second discharge reservoir via said fluiddrainer.
 18. The method of claim 17, wherein said apparatus furthercomprises a power supply, said zinc-air cell comprises auxiliarycharging electrodes and said power supply applies current to saidauxiliary electrodes.
 19. The method of claim 18, wherein the steps ofpromoting conveyance of zinc-containing electrolyte fluid from saidreservoir to said zinc-air cell via said export feed; and promotingconveyance of electrolyte fluid from said zinc-air cell to saidapparatus via said fluid drainer, precedes the step of applying currentto said zinc-air cell, thus allowing cleaning of zinc oxide from saidanode.
 20. The method of claim 18, wherein said power supply comprises aDC charger.
 21. The method of claim 18, wherein discharge of saidzinc-air cell is conducted in cycles such that: said zinc-air cell isonly partially discharged each cycle; the resultant zinc oxide producton the anode is cleaned off after each partial discharge cycle byflowing electrolyte from said reservoir; electrical charging by saidcurrent is commenced once every few cycles.
 22. The method of claim 17,wherein said method comprising zinc regeneration from zinc oxide in saidregeneration unit, wherein said zinc regeneration comprises theformation of zinc on said cathode and the oxidation of hydrogen on saidanode.
 23. The method of claim 22, wherein said hydrogen is supplied tosaid anode by reforming of natural gas.